The present invention relates generally to radiographic imaging and, more particularly, to a method and system of detecting colon polyps in a colorectal region of a subject without cathartic preparation or insufflation of the colorectal region. The present invention also relates to a method and system of automatically detecting an embolism or thrombus in normal vascular tissue. The present invention is particularly applicable with photon counting and/or energy discriminating CT systems.
Colorectal cancer is a leading cause of cancer deaths. There are several accepted screening techniques that have been developed for the detection of potentially cancerous polyps. It is widely recognized that if these polyps can be detected and removed, the incidence and mortality rates of colorectal cancer may be reduced.
Furthermore, misdiagnosis often occurs in detecting abnormalities such as an embolism, a thrombus, or a blood clot in complicated blood vessel structures. Because of blockage in a blood vessel, vascular structure beyond the abnormality cannot receive contrast agent and may not be visible. If such abnormalities can be detected more efficiently, the incidence of misdiagnosis may be reduced.
Endoscopic colonoscopy is a common technique employed to detect potentially cancerous polyps. Colonoscopy, however, is an invasive and frequently uncomfortable experience for a patient. Recently, other techniques such as CT colonography, in which the principles of computed tomography is used to image the entire colon or colorectal region of a patient, have been developed and shown to be highly sensitive in the detection of these potentially cancerous polyps. While a CT colonography exam is considered much less invasive than a colonoscopy, CT colonography requires a cathartic bowel preparation, stool marker, and/or insufflation of the colon to capture contrast between polyps and stool in an image. While most patients do not experience complications from this cathartic preparation, the procedure can be highly disagreeable and is noted as a significant factor for patient non-compliance with screening regimens.
Furthermore, insufficient preparation can lead to fluid or stool retention which can obscure findings. As a result, it has been recommended that two exams be taken: one in the supine position and one in the prone position. Acquiring CT data when a patient is in the prone position allows for any residual fluid to collect at the bottom and allow a radiologist to uncover any polyps that may have been masked by the fluid when the patient was in the supine position. While taking two examines improves overall detection rates, it increases scan times and decreases patient throughput.
Recent advances in CT imaging include faster scanning speed, larger coverage, and higher power x-ray tubes. These improvements have enabled, for instance, the continuous scanning of the thorax in a single breath hold and continuous scanning of the vascular structure in the legs. These recent technological advances have improved the detection of pulmonary embolism (PE) and deep venous thrombus (DVT).
CT images may be enhanced by use of a contrast agent such as iodine to enhance the conspicuity of blood vessels in detecting PE and DVT. Using CT, the vascular structure can be distinguished from other tissue because of the high contrast between the contrast agent with respect to background tissue, which is mostly water. In some instances, though, the blood vessel can be blocked by an embolism, thrombus, or blood clot. Such blockage prevents the tissue beyond the blockage from receiving contrast agent, resulting in tissue beyond the thrombus that is not visible against the background tissue. In such cases, the radiologist must recognize anatomy within the image where the vascular structure is missing, and then must look for the cause of the blockage.
Because of the difficulty in determining a location of a thrombus, misdiagnosis can occur in identifying PE and DVT. As an example, in order to review the chest, a medical practitioner or radiologist may have to review 100-300 high resolution axial images, and the difficulty is exacerbated because over half of PE cases are diagnosed in an emergency situation.
It would therefore be desirable to design a CT system capable of imaging a colorectal region of a subject with contrast between polyps and stool without cathartic preparation or insufflation thereof. It would also be desirable to design an apparatus and method that quickly, easily, and automatically identifies possible PE and DVT in a CT image to a radiologist.